1. Field of the Invention
This invention relates generally to the controlled filling of the catalyst tubes of catalytic reactors with catalyst materials when the reactors are placed into service or when they have been cleaned of spent catalyst materials in preparation for further use in processes requiring catalytic reaction of flowing products of the process. More particularly, the present invention concerns a mechanized catalytic reactor charging system including a loading cart that is used by reactor servicing personnel and which is effective for efficient and controlled and simultaneous charging of a plurality of the reaction tubes of a catalytic reactor so that each of the plurality of reaction tubes will contain a precise measured quantity of the catalyst arranged in one or more layers and having a predetermined degree of compaction. Even further, the present invention concerns a mechanized catalyst loading cart having the capability for automatically adjusting the amplitude of vibratory movement of a dispensing control tray thereof with respect to the weight of catalyst material contained therein for dispensing, so as to ensure the consistent measured and timed dispensing of the catalyst material during a complete dispensing cycle of the loading cart. This invention also concerns a method and apparatus for the mechanized filling of catalyst charging hoppers at a location remote from the tube sheet of the reactor and for efficiently and safely charging the catalyst loading cart with catalyst material from the catalyst charging hoppers.
2. Description of the Prior Art
Although, for the purpose of discussing the preferred embodiment of the invention disclosed herein, the present invention is discussed particularly as it relates to the dispensing of measured quantities of catalyst material into the reaction tubes of catalytic reactors, it should be borne in mind that the invention may be employed for the dispensing of measured quantities of other materials for other purposes. Thus the scope of the present invention is not intended to be limited by the specific discussion of the preferred embodiment, but rather the preferred embodiment of this invention is intended only as a representative example that comes within the spirit and scope of the invention.
In a chemical plant the desired chemical is generally manufactured with the use of a tube and shell type catalytic reactor. The typical catalytic reactor is a cylindrical structure approximately 15' in diameter and can be 100' or so in height (all catalytic reactors are custom designed and built for a particular chemical process and thus can have a wide range of diameters and heights). The reactor is typically in the form of a cylindrical shell having domed and flanged top and bottom ends that are unbolted and removed to permit servicing of the reactor. A multiplicity of reaction tubes are typically located vertically in the reactor and have upper and lower ends that are welded to upper and lower tube sheets that extend transversely of the reactor shell and are located adjacent the end flanges of the reactor shell. The reaction tubes are typically in the order of 1" in diameter and are welded to the tube sheets in a geometric pattern. A worker standing on the upper tube sheet will visualize a flat sheet having a multiplicity of holes arranged in a geometric pattern and being about 1/2" apart, with each hole having a weld bead about it for connection of the upper tube end to the upper tube sheet.
One or more types of catalyst material is loaded into each of the reaction tubes and is provided in the form of small spheres or cylinders in the range of from 1/16" to 1/2" in diameter. The catalyst pellets are typically composed of ceramic or alumina material that is coated with a reactive agent for the process that is intended. Upon activation in the presence of a fluid flowing through the reaction tubes the catalyst reacts with the flowing fluid to give off a derivative product. Generally, the catalyst is loaded into the reaction tubes (some up to 20,000 tubes) in zones or layers. That is to say, if the reaction tube is 60' in height, catalyst "A" would comprise a 20' zone, catalyst "B" would comprise a second 20' zone and catalyst "C" would comprise a third 20' zone. The loading rate of the catalyst into these tubes determines the compaction of the catalyst within the tubes. This is referred to as "drop time". The space remaining within the tubes which is above the upper end of the catalyst is referred to as "tube outage". Ideally, if all (20,000) tubes have the same "drop time" during charging or loading thereof, the tube outage (the balance of unfilled tube) will be uniform. When the reactor tubes are all charged uniformly it will yield the best reactor performance, i.e., the best quality and quantity of resulting chemical product.
At the present time most catalyst loading or charging operations are conducted by completely manual activities, with workers using a funnel to direct catalyst pellets into a selected reaction tube as the catalyst is poured by hand from small premeasured bags. It is well known that each worker of a charging crew will typically pour catalyst pellets at a slightly different rate so that the result can often be poor drop time uniformity thus resulting in uneven tube outages. In some cases the catalyst pellets will bridge within some of the reaction tubes due to non-uniform drop time and catalyst compaction, thus resulting in voids that cause "hot spots" and uneven fluid pressures and temperatures within the various tubes of the reactor. The resulting chemical product from reactors that have not been uniformly charged with catalyst is often less than optimum quality.
Various attempts have been made to provide a mechanized catalyst loader and method of filling catalytic reactor tubes with pellets of catalyst materials. One example is presented by U.S. Pat. No. 3,223,490 of Sacken, et al wherein a plate is drilled to the same pattern as the holes of the reactor tubes and corresponding fill tubes are dependent from the plate so as to be loosely received within respective reactor tubes. The catalyst material is then dropped through the fill tubes into the reactor tubes until the level of the catalyst in each of the reactor tubes reaches the level of the fill tubes. Thereafter, the plate and its fill tubes are lifted so that the remaining catalyst pellets in each of the fill tubes will be deposited into the reaction tubes. This type of controlled filling achieves virtually the same catalyst bed height in each of the reactor tubes but it does not take into consideration the problem of catalyst pellet bridging and compaction within the respective reaction tubes. Thus, though the upper end of the catalyst beds in the tubes can be virtually the same, voids within part of the reaction tubes which occurs by uncontrolled drop rate will result in uneven catalyst materials in the catalyst beds. Further, this method does not provide for consistent drop rate of the catalyst so that uneven tube outage and non-uniform compaction can be the result. This could result in the development of hot spots within the reactor which could be detrimental to reactor operation. Also, since virtually every reactor is "custom designed" so its height, diameter and number of catalyst reactor tubes can vary, clearly the catalyst loader shown in this patent must also be "custom designed", for the reactor hole pattern and dimension of the reactor. Thus, a catalyst loader of this nature would need to be dedicated to this particular reactor so that a catalyst loader would be needed for each reactor. It is desirable therefore to provide for catalyst loading operations by means of mechanized catalyst loading which is readily adjustable to the hole pattern and tube dimension of various types of catalytic reactors.
A catalyst loading cart mechanism is presented by U.S. Pat. No. 4,402,643 of Lytton, et al which has a plurality of catalyst storage hoppers each feeding a respective slot of a vibratory tray, with the catalyst pellets dropping from the tray into respective flexible conduits that are engaged within the upper openings of a plurality of reaction tubes. This apparatus has proved ineffective because the vibratory activity of the tray does not ensure precision control of the drop rate of the catalyst pellets from each of the feed grooves of the tray. Use of this apparatus has been discontinued as ineffective for simultaneous loading of multiple catalytic reactor tubes.
Another prior art reactor tube loading device is disclosed by U.S. Pat. No. 4,701,101 of Sapoff, wherein a catalyst loading funnel is provided having a plurality of generally triangular storage chambers which feed catalyst fill tubes that are inserted into the openings of a plurality of reaction tubes. The funnel mechanism may be supported by a wheeled cart and provided with flexible tubes having tubular spouts at the lower ends thereof which are received within the openings of a plurality of reaction tubes. The drop rate of the catalyst material is intended to be adjustable by adjusting the speed of rotation of metering rods or by raising and lowering metering rods in each funnel module to increase or decrease the speed of catalyst drop.
Although catalytic reactors for chemical processes may take various forms, for purposes of the present invention the reactors of particular concern are fixed bed type catalytic reactors having an external housing or shell of considerable height within which is mounted a multiplicity of reaction tubes, the tubes being supported at the upper and lower ends thereof by means of tube sheets. The reaction tubes may also be provided with intermediate support if appropriate for the structural integrity of the reactor mechanism. The catalytic reactors typically utilized in the petroleum and petrochemical industries typically employ reactor tubes having an internal diameter in the order of one inch and a length in the order of from 60' to 100' or more. Depending upon the character of the reaction to occur, the reactor tubes may be filled to a predetermined level with pellets of catalyst material so that the outage (the space above each tube bed of catalyst) will be substantially the same. In many cases, each reactor tube will contain two or more catalyst materials each arranged to a predetermined fill level. For efficient operation of catalytic reactors, each of the reaction tubes should be loaded with catalyst pellets in precisely the same way so as to obtain consistency of catalyst arrangement and compaction within each of the reaction tubes. Typically, catalytic reactors are loaded or charged by means of a highly labor intensive manual loading operation. In this case, workers are present at the upper tube plate of the reactor, where the openings of the multiple reaction tubes are exposed. These workers utilize funnels having lower discharge tubes that are inserted into the tube opening of a reaction tube to be filled. These tube filling personnel are typically trained to deposit reactor pellets into the funnel and thus, into the reaction tube in accordance with a predetermined quantity input which is referred to as "drop time" or "drop rate". If the quantity input of the catalyst is exceeded, it is possible that the catalyst pellets can bridge within the tubes, thereby developing voids in the catalyst beds of some of the tubes and thus resulting in uneven outage at the upper ends of some of the tubes. The character of catalyst input to the various tubes of a reactor is also determined by the character of the catalyst being loaded. Catalyst materials are provided in spherical pellets of various size and are also provided in cylindrical pellets of varying size. The respective pellets whether cylindrical or spherical must be dropped into the tubes in accordance with a particular timing sequence "drop time" so that the resulting catalyst bed in each of the tubes will be virtually the same and the outage at the tops of the tubes will also be virtually the same.
The upper and lower ends of a cylindrical reactor shell are typically closed by means of domed closures that are secured by bolts to upper and lower connector flanges of the reactor shell. For catalyst loading, the upper domed closure is typically unbolted from the catalyst shell, is lifted therefrom by means of a crane and is typically lowered to the ground until the tube filling procedure has been completed. To facilitate loading of the catalyst materials into the multiple reaction tubes of a catalytic reactor, a temporary "working compartment" of sufficient height for a worker to stand on the upper tube sheet of a reactor is assembled to the upper end of the reactor shell. This enclosure is typically air-conditioned for the comfort of workers and is provided with a dust removal system to ensure as much as possible that catalyst dust, that is typically liberated into the atmosphere during the charging operation, is continuously removed from the working enclosure. Further, the workers engaged in the loading operation typically wear sealed outer garments that prevent the catalyst dust from coming into contact with the worker's skin and also wear ventilation equipment to ensure the that the catalyst dust is not breathed by the workers.
Obviously, manual loading of catalyst materials by means of funnels as is currently done, is subject to many disadvantages. For example, the labor requirements for a manual catalyst loading operation add significant cost to the reactor and thus add to the cost of the resulting product. It is therefore desirable to provide for mechanized catalyst loading operations that significantly minimize labor costs. Since hand loading of catalyst materials is subject to wide variation of drop time, catalyst compaction, etc., depending upon the catalyst materials being used and the workers accomplishing the loading operation, it is desirable to provide a mechanized catalyst loading operation to enable precision loading of each of the catalyst tubes of the reactor so that the resulting catalyst bed in each of the tubes is virtually the same and the outage between the catalyst bed and the tube sheets of the reactor is also virtually the same. Tests which have been conducted indicate clearly that mechanized catalyst loading is much superior in comparison with hand loading of catalyst materials because the drop rate of the catalyst materials can be efficiently controlled so that the drop rate is the same with each of the catalyst materials within each of the reaction tubes.
From the inventor's studies concerning loading operations for catalytic reactors, virtually any phase of the catalyst handling and reactor loading operations where manual operations are used, the results of such operations can be improved by mechanization, thus achieving repeatability and better productivity. Thus, according to the present invention is desirable to provide a catalyst handling, measuring and catalytic reactor charging system that as much as possible takes advantage of mechanization and minimizes the manual aspects of catalytic reactor servicing operations.